Circuit interrupter



Oct- 9, 1934- H. L. RAwLlNs CIRCUIT INTERRUPTER v Filed April 8, 1933 2 Sheets-Sheer,- 1

ATTORNE afa' 75 65 65 E555 Oct. 9, 1934. H. L. Ru\w1 n-lsv CIRCUIT INTERRUPTER 2 Sheets-SheetA 2 Filed April 8, 1953 3 lNvNToR Herbe/ L. RaW/075 A'TTohNE Patented Oct. 9, 1934 UNITED STATES CIRCUIT INTERRUPTER Herbert L. Rawlins, Wilkinsburg, Pa., assignor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application April 8, 1933, Serial No. 665,132 3i claims. (crece- 120) My invention relates to circuit interrupters and particularly to high voltage expulsion fuses.

One object of my invention is to provide a rellable high voltage expulsion fuse that shall be simpler in design, more economical to manufacture, and more satisfactory and more reliable in operation than the previously known devices of this general type.

Another object of my invention is to provide an improved refill element for use with expulsion fuses, my improved rell element to be inexpensive to manufacture and simple to install.

A further object of my invention is to provide an improved high voltage expulsion fuse which shall include at least two separate arc passages and means for establishing an arc in each of the passages, the arc interrupting capacity of the two passages being different in order that the fuse may be equally effective for both high and low values of arc current.

A further object of my invention is to provide an improved expulsion fuse of the double arc passage type which shall include means for establishing one of the two arcs at a time subsequent to the establishing of the other arc.

A further object of my invention is tov provide an improved lining for the arc passage of an expulsion fuse, my improved lining to liberate a large volume of non-inflammable arc-extinguishing gas, substantially all of which is of inorganic composition, when placed in proximity to an electric arc, and to 'include means for strengthening those parts of the lining which may be mechanically weak. 35 A still further object of my invention is to provide an improved expulsion fuse which shall utilize a fuse link of small dimensions positioned adjacent the open end of the fuse closure, and which shall include means for drawing the arc within the closure during the extinguishing operation.

One field for immediate application of my invention is in connection with high voltage expulsion fuses that utilize boric acid as the source of the arc extinguishing gas, and I shall hereinafter describe an 'embodiment of my invention as appled to such devices, without, however, in any way intendingto restrict the scope of my invention except as indicated in the appended claims. y

In this type of fuse, a short fusible link is connected to the lower end of a movable rod or plunger, the other end of the rod being aflixed to a piston member of conducting material which 5 is disposed within an insulating tube and is biased upwardly by a coil spring. A exible conducting shunt disposed within the coil spring completes the electrical circuit to the stationary Contact. Upon the fusion of the link, the rod moves upwardly, under the influence of the biasing spring, and establishes the arc Within a chamber that is lined with boric acid. The boric acid decomposes and the resulting outwardly ilowing vapor, substantially all of which is superheated steam, extinguishes the arc.

The fuse is restored to an operative condition following each circuit interrupting operation by the removal and replacement of the refill element which includes the boric acid lining for the arc passage, the movable plunger, and the fuse assemblage. From this, it is immediately apparent that the rell operation consists in the replacing of all of the parts which are subjected to the action of the arc, thereby assuring continued reliable operation of the device.

The features of my invention which I believe to be new are particularly pointed out in the appended claims. For a fuller understanding of the principles of the invention and the best mode of applying those principles, reference may be had to the accompanying drawings, in which;

Figure l is a side view, partially in section, of an expulsion fuse embodying the principal features of my invention.

Fig. 2 is an enlarged sectional View of a refill element for use with the expulsion fuse shown in Fig. 1.

Fig. 3 is a sectional view similar to Fig. 2 showing a modified form of refill unit.

Fig. 4 is an enlarged sectional view on the line IV--lV of Fig. 1.

Fig. 5 is an enlarged end elevation of the expulsion fuse shown in Fig. 1.

Fig. 6 is an end elevation of one of the refill units shown in Figs. 2 and 3.

Fig. 'i is a fragmentary sectional view showing the method of connecting the rell element and the movable piston member.

Fig. 8 is an end elevation of the fuse structure shown in Fig. 1 and illustrates the method used for supporting the operating spring.

Fig. 9 is a fragmentary sectional view showing the structural details of the upper end of the fuse shown in Fig. 1.

The expulsion fuse shown in Fig. l includes a cylindrical fibre tube 1, having relatively heavy side walls and threaded ends 3 and 5, and two tubular terminal caps 'I and 9 which have internally threaded portions for engaging the threaded ends 3 and 5 of the main nbre tube 1. 110

The terminal caps are each provided with contact surfaces 11 for engaging suitable contact jaws (not shown). The upper terminal cap 7 is provided with an annular recess 13 for engaging the upper portion of the outer tube 15 which is preferably of porcelain or glass, or other weatherproof insulating material. A projecting shoulder 17 on the lower terminal cap 9 holds the porcelain tube 15 within the annular recess 13, suitable washers 19 and 21 of cork or like material being provided for preventing undue stress being placed on the porcelain tube 15 and to make the joint'watertight. 'I'he upper end of the fuse is closed by means of a cap member 23 which, as will be described in some detail later, engages the support means for the main operating spring 25.

The working parts of the fuse include the main operating spring 25 which is provided with a support member 27 at one end and which engages the piston member 29 at the other end, the exible conducting shunts 31 disposed within the main operatingspring 25 and electrically connected to the spring engaging members 27 and 29, as shown particularly in Figs. 7 and 9, and the renll element 33 which engages the piston member 29. The lower end of the refill element 33 is provided with a ferrule 35 which is adapted to abut against a shoulder 37 forming a part of fill elementy 33 in position and to assure a good electrical contact between the ferrule 35 and the lower terminal cap 9 itself.

The preferred form of the rell element 33 is 4shown particularly in Fig. 2. It includes a fibre tube 45 having side Walls of considerable mechanical strength and a threaded end 47 for engaging the metallic ferrule 35. The bre tube 45 is lined for thegreater partof its length with a cylindrical lin'er member 49 of boric acid. The boric acid lining has a cylindrical passage 51 through 'the center in order to accommodate the rod or plunger 53, and is further provided with a second passage 55 of considerably smaller cross sectional area than the passage 51.

A threaded fibre plug 57 having an opening 59 therethrough is provided for engaging the upper end of the boric acid lining 49, an insulating washer 58 being interposed between the plug' 57 and the lining to equalize the stresses. The lower end of the central passage 5l terminates in a conical throat 60, the lower portion of which is defined by a nbre plug 61, it being necessary to provide a material of greater mechanical strength than boric acid for lining those por tions of the throat where the thickness of the lining becomes small. The ferrule 35 is provided with an opening 63 which forms a continuation of the central passage 51 and the throat 60, and an annular shoulder 65 which abuts against an insulating washer 67 to retain the lining 49 within the tube 45.

The cylindrical plunger or rod member 53 is preferably of copper; the lower end 68 includes an opening (not shown) for permitting one end of the fusible link 69 to-be soldered thereto, the other end of the fusible link 69 being electrically connected to the ferrule 35 by means of a screw 71. rI'he upper end 70 of the plunger rod 53 is threaded for engaging the piston member 29, and is provided with 'a positioning pin 73 extending therethrough substantially at right angles to the longitudinal axis of the plunger, This pin 73, as shown particularly in Fig. 6, cooperates vwith two diametrically opposed slots 75 in the top In the modiiication of the refill unit 33 shown y in Fig. 2, a wire 77 of somewhat smaller cross sectional area than the cross sectional area of the smaller passage 55 through the boric acid lining 49 is securely aiiixed to the upper end 70 of the plunger rod 53 and extends downwardly into thepassage 55 where it slidably engages a similar wire 79 extending upwardly into the passage 55 for about one-third of its length. The lower end of the wire 79 is retained in position within a recess in the nbre throat lining member 6l and is not electrically connected to the ferrule 35.

The modification of the refill unit 33 shown in Fig. 3 is similar to the structure shown in Fig. 2 except that a single wire 81, rigidly affixed to the plunger 53 at the upper end thereof, extends through the .passage 55, the lower end of the wire"8l engaging a suitable recess in the throat lining member 61 and being therein retained by the insulating washer 67. The wire 81 includes a coil portion 83 for providing a lost motion connection between the portion within the passage 55 and the portion aflixed to the plunger rod 68. Thus, when the plunger 68 is movedupwardly by the piston member 29, the wire 81 does not move to establish an arc within the passage 55 until a time subsequent to the establishing of the arc in the central passage 53. In the modication shown in Fig. 2, this time delay is secured by means of the sliding en gagement between the wire 77 mechanically connected to the moving plunger 53 and the other wire 79. The current carrying capacity of the wires 77 and 78 is limited in order that they may fuse upon the passage therethrough of current of a predetermined magnitude, this arrangement facilitating the interruption of high current arcs.

The lower end of each of the rell units 33 is closed by means of a frangible disk 85 of insulating material. This disk 85 is adapted to break immediately upon the building up of any appreciable gas pressure within the unit, and, while it ,Y

completely seals the Vent end of the refill it in no way interferes with the normal expulsion action of the device.

The piston member 29, as is shown particularly in Figs. 1 and 7,l include a body portion 87, a

threaded opening 89 for engaging the threaded end 70 of the refill element 33, a similar threaded opening 91 at the upper end for engaging the screw 93 which cooperates with a wedge member 95 to fasten the conducting shunts 31 to the body portion 87, and a threaded means 97 on the outer surface for securely engaging onen tion with the spring supporting member itself,

and, in addition, it includes a threaded end portion 107 having a pin 109 extending therethrough (Figs. 8 and 9.). This threaded end portion 107 cooperates with the cap member 2,3 in order to hold the spring 25 in the tensioned or operative spring 25.

position and, at the same time, permits the establishing of a low resistance electrical connection between the upper end of the shunts 31 and the upper terminal cap 7, the spring supporting member 27 having a shoulder 111 which cooperates with a similar shoulder 113 on the inside of the upper terminal cap 7.

The fuse is shown in the closed circuit position in Fig. 1. It will be noted that the main operating spring 25 is tensioned so as to bias the piston member 29 toward the upper terminal cap 7. This biasing` force is transmitted through the plunger 53 and must be balanced by the fusible element 69. Upon the occurrence of an overload condition in the controlled circuit, the fusible link 69 melts, thus releasing the lower end 68 of the plunger 53 and permitting that member to move upwardly into the central arc passage 5l under the biasing action of the main operating An arc is immediately established between the end 68 of the plunger 53 and the ferrule 35. This arc will. practically immediately contact the lower end of the wire 79 thereby putting the conductors '77 and 79 within the smaller of the two arc passages in parallel with the arc. If the current to be interrupted is of small magnitude, the immediate result wil be an extinction of the arc in the central passage 51 at the first zero point, all of the current flowing through the conductors 77 and 79, and further upward movement of the plungerl 53 will then result in a separation of the two wires 77 and 79 which are in slidable conductive relationship. A second arc will thereby be established within the smaller arc extinguishing passage 55 and, since that passage is particularly adapted for extinguishing small arcs, the out-owing superheated water vapor will cause a very rapid cooling and extinguishing of the arc.

If the magnitude of the arc current is such as to cause an immediate fusing of the conducting means within the smaller arc passage 55, the arc will persist in the larger passage 51, although the extinguishing operation. is essentially the same,

` the heat of the arc causing the boric acid lining 49 to evolve superheated steam which flows outwardly longitudinally of the arc through the throat opening 69, the opening (i3-in the ferrule,

and the continuation of that opening in the lower portion of the terminal cap 9 and the hollow cylindrical member 39.

One method utilized in the past to secure interruptions o small current arcs in expulsion fuses utilizing the double arc passage construction was to provide a fusible wire, having a lower rating than the main fusible element within the smaller arc passage. This structure was not entirely satisfactory, however, because when the fuses were used on high voltage circuits the destructive eiiect of corona upon the smaller dlameter fuse wires resulted in a very definite limiting of the minimum value of arc current which could be interrupted, that value for usual distribution voltage being somewhere around 40 amperes. With my invention, however, a positive mechanical opening of the electrical circuit within the smaller of the arc passages is secured, whether the conducting means disposed therein fuss or not, and it is possible thereby to interrupt arc currents of practically any range. In this connection, it'is important to note that it is not possible to satisfactorily interrupt low current arcs in the larger arc passage due to the absence of means for bringing the arc into intimate contact with the gas evolving lining of the arc passage.

The operation of the modification shown in Fig. 3 is essentially the same as the operation of the structure shown in Fig. 2, except that the establishment` of the arc in the smaller arc extinguishing passage 55 is caused by the mechanical movement of the lower end of the wire 81 from its engagement with the fibre lining member 61 and the drawing of the wire 81 through the smaller passage. The coil portion 83 of the wire 81 makes possible a time delay between the fusing of the main fusible element 69 and the drawing of the arc in the smaller arc passage 55.

Following each circuit interrupting operation of the expulsion fuse, it is necessary to restore the device to an operative condition., This is accomplished in. the preferred embodiment of my invention by the replacing of the refill element 33, thereby renewing all of the parts of the fuse which come in contact with the arc and which may thereby be damaged. The refill element 33 is relatively inexpensive, however, d ue to its simple structure, and while it makes possible the restoration of the fuse to a potential effectiveness equal to that when new, the cost of so doing is much less thanJ the cost of restoring any of the previously known high voltage expulsion fuses to an operative condition.

In the open circuit position, the plunger member 53 has been moved by the operating spring 25 a sufficient distance toward the upper end of the fuse to draw the end of the plunger to the vtop of the central arc extinguishing passage 51.

.'Ihe rst step in the insertion of a new -rell element 33 consists in the unscrewing of the cylindrical retaining member 39 which screws into the lower portion of the terminal cap 9. The fibre tube 45 which forms the body portion of the rell element 33 and its attached ferrule 35 are then free to drop out, leaving only the plung"v er 53 within the fuse tube. In order to remove the plunger 53 and to rensert the new rell element, the cap member 23 on the upper terminal cap 7 is unscrewed from the threaded portiony 107 of the spring supporting member 27, rotation of that member being prevented by the engagement of the pin 109 with the slot 115 in the top of the upper terminal cap 7.

Following the removal of the cap 23, the spring supporting member 27 may be lifted upwardly and turned in a counterclockwise direction (Fig. 8) so that the pin 109 alines with the slotted openings 117 extending entirely through the upper portion of the terminal cap '7, The spring supporting member 27, the spring 25, the piston member 29, the associated shunts 31, and the plunger 53 which is screwed into the piston member 29 may then be removed from the lower end of the fuse mechanism. The nextA step is the -removal of the plunger 53 from the piston member 29. Following this, a new refill element 33 is screwed securely into the piston member 29, the pin 'i3 preventing rotation of the plunger member 53 with respect to the body portion of the reiill element. The connected rell element and plunger moving mechanism are then inserted in the lower end of the fuse and the cylindrical retaining member 39 is tightened so as to securely hold the ferrule 35 of the rell element 33 against the cooperating shoulder 37.

In order to tension the spring 25, it is now necessary to insert a means for engaging the spring supporting member 27 into the fuse through the openingr 119 in the upper terminal suitable threaded end for engaging the threaded hole 121 in the top of the spring supporting member 2'7. The rod or other means for engaging the spring supporting member 27 is screwed into the threaded opening 121 and the spring supporting member 27 is then pulled upwardly toward the top terminal cap 7, it being necessary to aline the pin 109 with the slots in order to draw the threaded portion 107 of the member 2'7 through the opening 119. The spring support member 27 is then rotated in a clockwise direction in order to permit the reengagement of the pin 109 with the stops 123 which prevent that member from disengaging the end terminal cap '7. The cap member 23 may then be screwed onto the `threaded end-107 of the spring supporting member 27, thereby eifectively closing the upper end of the fuse and restoring the entire device to an operative condition.

It will thus be seen that I have disclosed an improved high voltage expulsion fuse which is of simple design and which at the same time, is capable of more satisfactory and more reliable operation than the structures heretofore known to the art.

In addition, it will be seen that I have disclosed an improved rell element for an expulsion fuse which permits the replacement, at a very mod- "erate cost, of all of the parts of the fuse which are exposed to the action of the arc. Further, I have disclosed means particularly adaptable for use With an expulsion fuse having at least two arc extinguishing passages of different arc interrupting capacities, whereby the arc in 'one of the passages may be established at a time subsequent to the establishing of the arc in the other of the passages through the use of a single, simple o erating mechanism.

Besides these features capable of wide adaptation to the expulsion fuse art, I have disclosed certain specific forms of construction which are particularly eifective incarrying out the general objects of my invention. I have shown how to reeniorce the lining for an arc passage with a material having greater mechanical strength than the lining itself, and I have shown a simple and effective means for connecting the operating spring of a plunger operated circuit interrupting device to one of the terminals of that device.

While, in accordance with the patent statutes, I have given the foregoing details of a preferred practical embodiment of my invention, it is to be understood that many variations from the precise form described are possible and may for some applications be desirable. I desire, therefore, that the language of the accompanying claims shall be accorded the bdoadest reasonable construction and that my invention be limitedy arc in one of said passages, and means, mechanically actuable by said means for establishing an arc in one of said passages, for establishing an arc in the other of said passages, one of said passages having a greaterarc interrupting capacity than the other of said passages.

2. In a device for interrupting an electrical circuit, a single means having a pair of passages therein, said passages each providing a path for an arc, said arc paths being arranged electrically in parallel in the circuit to be interrupted, means for establishing an arc in one of said passages, and means, mechanically actuable by said means for establishing an arc in one ofsaid passages, for establishing an arc in the other of said passages at a time subsequent to the establishing of said rst arc, one of said passages being most effective in extinguishing arcs of low current value and the other of said passages being most effective in extinguishing arcs of high lcurrent value.

3. In a device for interrupting an electrical circuit, a, single wall defining means having a pair of passages therein, means, mechanically interconnected, for establishing an arc in each of said passages, and means for electrically connecting said arcs in parallel, one of said passages having a cross sectional area greater than the cross sectional area of the other of said passages.

4. In a device for interrupting an electrical circuit, a, single wall defining means having a pair of passages therein, means, mechanically interconnected, for establishing an arc in each of said passages, and means for electrically connecting said arcs in parallel, said arc establishing means including means whereby an arc is established in one of said passages before the second arc is established in the other of said passages.

5. In a device for interrupting an electrical circuit, a single means for defining a pair of passages having rigid walls, means including a plunger and a member of conducting material, each movableA in one of said passages, for establishing an arc in each of said passages, said movable plunger and said movable member of conducting material being mechanically interconnected, and means for electrically connecting said arcs in parallel, each of said passages having a cross sectional area only slightly greater than said arc establishing means movable therethrough.

6. In a device for interrupting an electrical circuit, a single means having a pair of passages therein, a plunger movable in one of said passages to establish an arc therein, means movable in the other of said passages to establish a second arc in said other passage, a lost motion mechanical connection between said plunger and said movable means whereby said second arc is said first arc, and means for electrically connecting said arcs in parallel, one of said passages having a substantially greater cross sectional area than the other of said passages, and both of said passages being lined with a solid material capable of evolving large amounts of gas when placed in proximity to an electric arc.

'7. In a device for interrupting an electrical circuit, means having a pair of passages therein, a plunger movable in one of said passages to establishan arc therein, means movable in the other of said passages to establish a second arc in said other passage, a lost motion mechanical connection between said plunger and said movable means whereby said second arc is'established subsequent to the establishment of said rst arc and means for electrically connecting said arcs in parallel, both of said passages being lined with boric acid.

8. In a device for interrupting an electrical circuit, means having a pair of passages therein, means mechanically interconnected, for establishing an arc in each of said passages, and

means for electrically connecting said arcs in parallel, both of said passages being lined with boric acid.

9. In a device for interrupting an electrical circuit, a single means defining a pair of passages, and means for drawing an arc in each of said passages, one of said arc drawing means including means which separate to establish an arc therebetween, the other of said arc drawing means including means adapted to slidably engage a cooperating means to delay the establishing of the arc in the other of said passages until a time subsequent to the establishing of the arc by said separable means.

10. In a device for interrupting an electrical circuit, means defining a pair of passages which have rigid walls and which are lined with a solid material capable of evolving an arc extinguishing gas when placed in proximity to an electric arc, and two separate means, mechanically interconnected for drawing an arc in each of said passages, one of said mechanically interconnected arc drawing means including a pair of conducting members which separate upon the occurrence of predetermined electrical conditions in the controlled circuit to establish an arc in the 'iirst of said passages, the other of said mechanically interconnected arc drawing means including a pair of conducting members which slidably engage each other during a portion of the arc drawing operation, the slidable engagement of said other arc drawing members causing the arc in the second of said passages to be established subsequent to the establishment of the arc in the iirst of said passages.

11. In a device for interrupting an electrical circuit, means defining a pair of passages which have rigid walls and which are lined with a solid material capable of evolving an arc extinguishing gas when placed in proximity to an electric arc, terminal means of conducting material positioned at one end of said passage deiining means, conducting means electrically connected to said terminal means and extending into the first of said passages for a predetermined distance, plunger means movable through the second of said passages to establish an arc therein, means mechanically connected to said plunger means and adapted to slidably engage said means extending into the first of said passages to establish an arc therein, and means for electrically connecting both of said arcs in parallel, the slidable engagement between said means extending into the iirst of said passages and said means mechanically connected to said plunger causing the are in the iirst of said passages to be established subsequent to the establishment of the arc in the second of said passages.

12. In a device for interrupting an electrical circuit, means defining a pair of passages, one of said passages having a greater arc interrupting capacity than the other of said passages, terminal means positioned at one end of said passage deiining means, conducting means extending into the passage of lesser arc interrupting capacity for a predetermined distance, plunger means movable through the passage ofA greater arc interrupting capacity to establish an arc therein, means mechanically connected to said plunger means and adapted to slidably engage said means extending into the passage of lesser arc interrupting capacity to establish an arc therein, and means for electrically connecting said arcs in parallel, the

slidable engagement between said means extending into the passage of lesser arc interrupting capacity and said means mechanically connected to said plunger causing the arc in the passage of lesser arc interrupting capacity to be established subsequent to the establishment of the arc in the passage of greater arc interrupting capacity, both of said passages being lined with material capable of evolving large amounts of gas when placed in proximity to an electric arc.

13. In a device for interrupting an electric circuit, means partially of compressed boric acid and partially oi' insulating material of greater mechanical strength than boric. acid, for deiining a passage having rigid walls, and means for establishing an arc within said passage.

14. In a device for interrupting an electric circuit, means, partially oi a solid material capable of evolving a readily condensible, inorganic gas when placed in proximity to an electric arc, and partially of insulating material of greater mechanical strength than said gas evolving material, for defining a', passage having rigid walls, and means for establishing an arc within said passage.

15.l In a device vfor interrupting an electric circuit, means of compressed boric acid for deiining a passage of substantially uniform cross section and having rigid walls, said passage having an enlarged throat portion at one end, means ofinsulating material of greater mechanical strength than said boric acid for defining a continuation of said throat portion, and means for establishing an arc in said passage.

16. In a device for interrupting an electrical circuit; a tubular closure; a renewable refill unit which is normally positioned within said closure and which includes means defining an arc passage and conducting means movable through said passage to establish an arc therein; and means within said tubular closure for releasably engaging and actuating said conducting means movable through said arc passage.

17. In a device for interrupting an electrical circuit, a tubular closure, means for closing one end of said tubular closure, a renewable reiill unit which is normally positioned within said closure and which includes means deiining an arc passage and conducting means movable through said passage to establish an arc therein, spring means within said closure for moving said conducting means to establish an arc within said passage, means for releasably connecting one end of said spring means to said movable conducting means, and means for releasably connecting the other end of said spring means to said means for closing one end of said tubular closure.

18. In a device for interrupting an electrical circuit; a tubular closure of insulating material; a renewable refill unit which is normally positioned within said closure and which includes a second tubular closure, the walls of which are i135 lined with a solid material capable of evolving large quantities of arc extinguishing gas when exposed to an electric arc; conducting means movable through said second tubular closure to establish an arc therein, and a fuse link for holding said conducting means in the closed circuit position; spring means within said first closure for moving said conducting means to establish an arc within said second closure following the release of said conducting means by said fuse link; and means for releasably connecting one end of said spring to said movable conducting means to permit the replacement of said rell unit.

19. In a device :for interrupting an electrical circuit, a tubular closure of insulating material, 15@

a renewable refill unit which is normally positioned within said closure and which includes a second tubular closure and conducting means movable through said second tubular closure to establish an arc therein, spring meanswithin said first closure for moving said conducting means to establish an arc within said second tubular closure, and means for releasably connecting one end of said spring means to said movable conducting means, at least a portion of the inner wall of said secondV tubular closure being of a material capable of evolving large volumes of an arc extinguishing gas, substantially all of which is of inorganic composition, when placed in proximity to an electric arc.

20. In a device for interrupting an electrical circuit; a tubular closure; removable means for closing one end of said tubular closure; a renewable refill unit which is normally positioned within said closure and which includes means defining an arc passage and conducting means movable through said passage to establish an arc therein; spring means Within said closure for moving said conducting means to establish an arc within said passage; means for releasably connecting one end of said spring means to said movable conducting means; and means at the other end of said spring means, engageable by a tool inserted through the end of said closure adapted to be closed by said removable means, to permit the stressing of said spring means and to releasably connect said other end of said spring means to said means for closing one end of said tubular closure.

21. In a device for interrupting an electrical circuit, a tubular closure, means for closing one end of said tubular'closure, a renewable refill unit including means defining an arc passage and con- 'ducting means movable through said passage to establish an arc therein; spring means within said closure for moving said conducting means to establish an arc within said passage, means for releasably connecting one end of said spring means to said movable conducting means, and means including a slotted opening in said means for closing one end of said tubular closure and rotatable means for cooperating with said slotted opening to releasably connect the other end of said spring means to said closing means.

22. In a device for interrupting an electrical circuit, means defining two arc extinguishing passages, the first of said passages being capable of interrupting low values of current, the second of said passages being capable of interrupting high values of current but being incapable of interrupting lo'w values of current, conducting means including a fusible wire within said first passage, and means operable after a predetermined period of time during the circuit interrupting operation to mechancally -withdraw said fusible conducting means for said first passage if said fusible conducting means has not previously fused.

23. In a device for interrupting an electrical circuit, means deiining two arc extinguishing passages, the first of said passages being capable of interrupting low values of current, the second of said passages being capable of interrupting high values of current but being incapable of interrupting low values of current, conducting means including a fusible wire within the first of said passages, means, actuable after a predetermined time during the circuit opening operation, for mechanically breaking the electrical circuit through said wire and withdrawing said Wire from said first passage if said Wire has not previously fused.

24. In a device for interrupting an electrical circuit; means for defining the walls of a pair of arc passages; one of said arc passages being capable of extinguishing arcs of large current magnitude but being incapable of extinguishing arcs of small current i iagnitude, and the other of said passages being c ,pable of extinguishing arcs of small current magnitude; and arc drawing means for causing the y circuit when carrying currents of large magnitude to |be 1in-ally interrupted in the first of said passages, and for causing the circuit when carrying currents of small magnitude to be finally interrupted in the second of said passages; said arc drawing mean-s comprising two separate conducting means one of which is movable through each of said passages to establish an arc therein, and a single means for moving both of said conducting means.

25. In a device for interrupting an electrical circuit; means for defining the walls of a pair of arc passages; one of said arc passages being capable of extinguishing arcs of large current magnitude but being incapable of extinguishing arcs of small current magnitude, and the other of said passages being capable of extinguishing arcs of small current magnitude; and arc drawing means for causing the circuit when carrying currents of large magnitude to ybe finally interrupted in the rst of said passages, and for causing the circuit when carrying currents of small magnitude to be finally interrupted in the second of said passages; said arc drawing means comprising two separate conducting means one of which is movable through each of said ,passages to establish an arc therein, and a single energy storing means for moving both of said conducting means; said arc drawing means causing the circuit through said interrupter to be initially opened in said arc passage capable of 'extinguishing `arcs of large current magnitude.

26. In a device for interrupting an electrical circuit; means for defining the wallsof a pair of are passages; one of said arc passages being capable of extinguishing arcs of large current magnitude but being incapable of extinguishing arcs of small current magnitude, and the other 0f said .passages being capable of extinguishing arcs of small current magni-tude; and arc drawing means for causing the circuit when carrying currents of large magnitude to be finally interrupted in the first of said passages, and for causing the circuit when carrying currents of small magnitude to be finally interrupted in the second of said passages; said arc drawing means comprising two separate conducting means one of which is movable through each of said passages to establish an arc therein, and a single means for moving lboth of said conducting means; said arc drawing means causing the arc which is established within said passage of lesser arc interrupting capacity to be established subsequentto the establishing of an arc within said passage of greater arc extinguishing capacity.

27. In a device for interrupting an electrical circuit; solid means of a material which is capable of evolving an arc extinguishing gas when placed in proximity to an electric arc for defining the walls of a pair of arc passages; one of said arc passages being so proportioned that it is capable of extinguishing arcs of large current magnitude but is incapable of extinguishing arcs of small current magnitude, and the other of said passages being capable of extinguishing arcs of 

